After nearly 15 hours of an extensive search for a 2-year-old boy dragged away by an alligator at a Disney resort, the Orange County sheriff said on Wednesday that there was “no question” that the boy was dead.

“We know that we are working on recovering the body of the child at this point,” the sheriff, Jerry L. Demings, said at a news conference. “We’re going to continue to search until we find the body.”

Nick Wiley, the executive director of the Florida Fish and Wildlife Conservation Commission, said, “We’re still hopeful that we can help the family find closure.”

The search, involving dozens of staff members from the sheriff’s office, the wildlife commission and Disney employees, began Tuesday night when the 2-year-old Nebraska boy was dragged away by an alligator at a lake at Disney’s Grand Floridian Resort and Spa.

“We’ve already taken four alligators and looked at four alligators and couldn’t find any evidence that they were involved,” Mr. Wiley said early in the search, adding that a fifth had been examined on Wednesday. “They had to be euthanized to be analyzed.”

The attack occurred around 9:15 p.m. on the beach of the Seven Seas Lagoon at the resort, Sheriff Demings said. The artificial lake, which is about 200 acres, is 14 feet deep in parts and feeds a series of canals that wind through the Disney complex. It lies across from Disney’s Magic Kingdom theme park.

Sheriff Demings said the search would continue until the body was found, and it was taking place in a man-made, sizable body of water. Mr. Wiley said there were experienced trappers on hand as well.

Sheriff Demings noted that Disney had operated there for 45 years and had never had a similar incident.

He added that 15 hours after witnesses saw the child taken under the water, it was not survivable at this point. “We know this is a recovery effort,” he added.

Jacquee Wahler, vice president of the Walt Disney World Resort, said the resort had closed its beaches for now.

“Everyone here at the Walt Disney World Resort is devastated by this tragic accident,” she said in an emailed statement. “Our thoughts are with the family. We are helping the family and doing everything we can to assist law enforcement.”

The boy was partly in the water at the edge of the lagoon with his mother, father and 4-year-old sister when the alligator pulled him away, the sheriff said.

“The father entered the water and tried to grab the child and was not successful in doing so,” Sheriff Demings said. He said the child’s mother might also have gone into the water to help. The father alerted a lifeguard, he said.

Jeff Williamson, a spokesman for the Orange County sheriff’s office, said the lifeguard on duty was “too far away, unfortunately.” The father “was able to get over there quickly and a struggle did ensue,” Mr. Williamson said, adding that the father “had minor lacerations to his arm.”

Neither the boy nor the four other members of the family, who had been visiting the Orlando area since Sunday, have been identified.

“Of course, they are very shaken up, extremely shaken up,” Mr. Williamson said, while emphasizing that he had not spoken directly to the family. “There are some pictures we’ve seen of a really beautiful, happy family.”

“It is simply heartbreaking,” he added. “There is no other way to say it.”

Sheriff Demings said that no such attack had been recorded at the lagoon before and that no “nuisance alligators” had been reported in the area recently. Mr. Wiley of the wildlife commission said that alligator attacks were “not common at all” but that alligators were capable of moving across the land and under the water so fencing them off was not a feasible option.

The governor of Nebraska, Pete Ricketts, said he was praying for the family.

Alligators are widespread in lakes in Central Florida. In 2015, the area had its first reported fatal alligator attack since 2007. The body of a swimmer, James Okkerse, 61, of DeBary, Fla., was pulled from a lake in Volusia County, north of Orlando, and he was determined to have been attacked by a 12-foot alligator that was later shot and killed.

The county medical examiner found that the death of Mr. Okkerse, who had disappeared while swimming in Blue Spring State Park, was consistent with an alligator attack.

That same year, a 22-year-old man who law enforcement officials said was trying to avoid capture during a burglary was killed by an 11-foot alligator in Brevard County, east of Orlando. The man, Matthew Riggins, had drowned, the Brevard County Sheriff’s Office said, and his body showed signs of having been mauled. Divers from the sheriff’s office encountered an aggressive alligator that was trapped and killed.

The attack on the 2-year-old was the latest piece of grim news for the area, just days after a gunman declaring allegiance to the Islamic State carried out the worst mass shooting in United States history, killing 49 people at a gay nightclub in Orlando early Sunday.

On Friday night, Christina Grimmie, a former cast member of the reality TV singing competition “The Voice” and a viral YouTube star, was fatally shot after performing at a popular Orlando music venue.

“We’re doing our best to deal with all of the situations we have going on here,” Sheriff Demings said. “But our staff is very resilient,” he added, and “they’re very focused, if you will, on assisting this family.”